1. Field of the Invention
This invention relates to an exclusive-OR or an exclusive-NOR and/or a majority logic circuit.
2. Description of the Prior Art
A full adder is known as one of the elements that constitute an arithmetic circuit in a computer, or the like.
Such a full adder comprises a three-input exclusive-OR circuit and a three-input majority logic circuit. Among the exclusive-ORs, an Ex-OR is a logic circuit which produces an L level output signal when the number of input signals having an H level is even-numbered and an H level output when the input number is odd-numbered. Assuming that the three inputs are A, B and C and the output is Q, the logic can be expressed as follows: ##EQU1## When this logic is achieved by ordinary NAND gates or NOR gates, several gates must be combined and a large number of transistors must be used.
A three-majority logic circuit outputs an L level when the number of the input signals having the H level is 0 or 1 and outputs an H level when the number of the input signals having the H level is 2 or 3. This logic can be expressed as follows with the output being P: EQU P=AB+BC+CA
Therefore, a large number of transistors must be used, too, in the same way as the exclusive-OR.
Attempts have been made to reduce the number of necessary transistors by forming an exclusive-OR or a majority logic circuit by the use of transistors having negative conductance, but they involve the problems that specific transistors must be used to achieve said logic circuit and a large number of resistors are necessary. Accordingly, these attempts have failed to afford an integral structure of the exclusive-OR circuit and the majority logic circuit, thereby to reduce the number of necessary transistors.
The present invention is directed to providing an exclusive-OR circuit, a majority logic circuit and furthermore, a full adder, each having a reduced number of constituent devices by overcoming the drawbacks of the prior art described above and reducing drastically the numbers of transistors and diodes that have been necessary in the prior art logic circuits, while using existing transistors and diodes.